So I have two continents on the equator with a north-south mountain range. One has the mountain range roughly in the middle, while the other is on the east coast. The plate boundary for the east coast range is continental/oceanic while the other is continental/continental.

Both mountain ranges are new and likely similar to the Andes, though not quite as tall given that the planet is a bit larger than Earth so I imagine that this would have an effect.

That said if I look at any sources on deserts they suggest they cannot or should not form on low ground near the equator due to the low pressure zone causing too much rainfall. That said, if I go 10/15-30 n/s I end up with this weird banded desert where there is hot desert on either side of my continent with tropical savannah or steppes in the middle. I am making the assumption that near the mountains and especially where elevation is still somewhat high I can throw in hot desert a la Somalia or Chile even near the equator, but what about the continental interior? There are cold currents, winds away from the coast and a tall mountain range casting a shadow, I feel like I should be able to merge the desert, should I taper it in towards the mountains? Putting more towards the interior and tapering out towards the coast? Should I push the desert to like 5 degrees on either side and leave a thin band of savannah in the middle?

Pictured are my two continents, one with the desert already filled in and one that hasn't been laid out.

You can see prevailing winds and ocean currents. Plates are too faint to see in these pictures, the spacing is done per 30 degrees with 1 degree squares filled in. Black blobs are approximate locations of mountains while light blue is savannah, dark blue is rain forest and red is hot desert as from the exact color guide on the Koppen classification Wikipedia page.

Interested in any and all thoughts! enter image description here enter image description here

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EDIT: Forgot to mention that average planet wide temperature would ideally be about the same as Earth's +-2c at most, that being said this planet is orbiting a smaller star closer to the edge of the habitable zone but all else being equal we can assume this planet would receive slightly less energy but have a slightly thicker atmosphere which my best efforts have been to compensate for this and give it about the same overall climate as modern day earth if again not slightly cooler. It has much less seasonal variation having a slightly more circular orbit and a 10 degree axial tilt. I've done my best to still allow for thermohaline circulation though I'm not sure if my southern continent would allow for it but I made sure to allow for one circumpolar current by leaving the north clear. Happy to provide other pertinent information.


1 Answer 1

  1. Rain shadows are poorly defined in equatorial regions because there is not much wind there, so there is little movement of air to block; and the winds, such as they are, are chaotic.

  2. Most non-polar deserts are ephemeral structures; at some times they are deserts, at other times they are not deserts. As recently as five thousand years ago, the Sahara was a pleasant open grass savannah with plenty of trees, great lakes and many rivers. There were giraffes and elephants and hippos, and the people raised lots of cattle:

    Cattle herd in the Sahara

    Cattle herd in the Sahara. Picture by an unknown inhabitant of Tassili n'Ajjer who lived some four or five thousand years ago.

    Arabia, the same. Six thousand years ago it was lush with numerous rivers; nowadays it is not.

    And it's not only hot deserts. Cold deserts may be ephemeral too; there were mammoths on Wrangel Island up to four thousand years ago, whereas today it is a genuine desert, with only some 138 mm (5.4 inches) of precipitation per year.

  3. The point being that there is no good method of predicting where deserts have to be in your world¹. Deserts come and deserts go. If you look at a map of the Earth, a planet which we are supposed to know very well, and mark the deserts, you will find that six thousand years ago the map would have been very different; and six thousand years from now it will be very different again: while the continents and the mountains did not and will not change appreciably.

  4. In the end, if you want a desert somewhere, just plop it there. If you want grassland, put grassland. Just make sure to avoid putting conifer forests on the equator, or tropical jungle on the 50th parallel; but almost anything else is fair game.

¹) The only exceptions are very high plateaus and large land masses around the poles, which are almost guaranteed to be quite dry. But only almost guaranteed; ten million years ago even Antarctica had forests.


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